I brainfarted and had a hard time trying to
understand the instructions.
> Incrementing is just like counting with numbers: xx, xy, xz, ya, yb, and so on. Increase the rightmost letter one step; if it was z, it wraps around to a, and repeat with the next letter to the left until one doesn't wrap around.
I only managed to understand it by looking at solutions on the
subreddit, figuring out the correct behavior:
az -> ba, azzz -> baaa, azzzzz -> baaaaa etc.
I also sped up the test case containing `ghi` as initial password,
by looking for the leftmost invalid I, L or O and increase it,
replacing all following chars with `a`.
ghijklmn -> ghjaaaaa.
